1. Field of the Invention
This invention relates to an elevator control apparatus. More particularly, it relates to an elevator control apparatus, which accurately computes the present position of an elevator car even if a power failure occurs while the car is traveling.
2. Description of the Related Art
A number of microcomputers and LSIs have been put on the market because of their technological development in recent years. They are available at low price and are applied to elevator control apparatuses. These microcomputers and LSIs have been utilized as detecting devices and as arithmetic units to compute the present position of an elevator car. The biggest disadvantage of such a detecting device as compared with conventional mechanical detecting devices is that it is not capable of computing the present position of the car if a power failure should occur.
A conventional elevator control apparatus will now be described with reference to FIGS. 8 to 13. FIG. 8 is a view showing an overall configuration of the conventional elevator control apparatus. As shown in FIG. 8, a counterweight 12 is engaged with one end of a rope 13 and a car 11 is engaged with the other end of the rope 13. The counterweight 12 and the car 11 are suspended from a sheave 14, which is driven by a motor 15. Pulses are generated from a pulse generator 16 connected to the motor 15, and are transmitted to a counter circuit 17. A signal 17a is transmitted from the counter circuit 17 to a microcomputer 18 in order to undergo the processes required. Power is fed from a power supply 19 to an elevator control apparatus 10, which comprises such components as the motor 15, the pulse generator 16, the counter circuit 17 and the microcomputer 18. Numeral 20 indicates a plate. A first position detecting device (DZD) 21 and a second position detecting device (DZU) 22 are attached to the car 11. Output signals 21a, 22a of the first and second position detecting devices 21, 22 are respectively transmitted to both the counter circuit 17 and the microcomputer 18. Numeral 23 indicates a fixed floor and numeral 24 indicates the bottom floor. Numeral 25 indicates a bottom floor detecting device. An output signal 25a is transmitted from the bottom floor detecting device 25 to the microcomputer 18. Numeral 26 indicates a cam attached to the car 11.
In the conventional apparatus as described above, the information about the traveling distance of the car 11 is transmitted from the sheave 14 to the motor 15 and further to the pulse generator 16. Pulses proportional to the traveling distance of the car 11 are generated from the pulse generator 16. These pulses are counted by the counter circuit 17 and transmitted to the microcomputer 18 as the signal 17a. The microcomputer 18 computes, based on the received signal 17a, the present position of the car.
The microcomputer 18 performs required computations at regular operation intervals, for example, every 50 ms. The microcomputer 18 computes not only the present position of the car 11 but also sequence controls, which are required for general operations, such as for controlling calls from aprons or from inside the car 11 and for opening and closing the door of the elevator. The microcomputer further computes speed control of the motor 15 and so on.
Information about the present position of the car 11 is essential to controlling the elevator. The information is necessary to compute the remaining distance from the present position of the car 11 to the floor where the request for the elevator is made. It is also required for generating the command signal for a rated speed to that floor. The information further controls various indicators within the car 11 and at the aprons.
FIG. 9 is a block diagram showing the inside configuration of the microcomputer 18. As shown in FIG. 9, a CPU 91, an input port 92, an output port 93, a ROM 94 and RAM 95 are interconnected through a bus 97. A backup power supply 96, having an appropriate battery, is connected to the RAM 95.
The ROM 94, in the microcomputer 18 configured as above, stores a program for operating the elevator, a program for controlling the motor 15 speed, a program for computing the present position of the car 11, etc. The signal 17a from the counter circuit 17, the signal 21a from the first position detecting device (DZD) 21, the signal 22a from the second position detecting device (DZU) 22 and the signal 25a from the bottom floor detecting device 25 are respectively transmitted to the input port 92. FIG. 10 shows formats of the RAM 95, when a building has floors from the zero-th floor (the bottom floor) to the N-1st floor (the highest floor). For example, in the case where I=0 to N-1, FLHD(I) and FLHU(I) in areas 31, 32 indicate the point when the first position detecting device (DZD) 21 and the second position detecting device (DZU) 22 respond on the I-th floor. FLHL(I) in an area 33 indicates the addition average of the two points FLHD (I) in the area 31 and FLHU(I) in the area 32.
That is, EQU FLHL(I)=1/2[FLHD(I)+FLHU(I)]
where, FLHD(I) and FLHU(I) correspond respectively to an integration value of the number of pulses, which are generated from the pulse generator 16, when the car is hoisted up from the bottom floor, which is the standard floor for computation.
SYNC in an area 34 indicates the present position of the car with the number of pulses from the pulse generator 16. For example, if one pulse is generated from the pulse generator 16 every time the car travels a distance of 1 mm, the SYNC value is 12,385 when the moving car reaches 12,385 mm from the bottom floor.
FSY in an area 35 indicates the present floor of the car in relation to all the floors of the building. For instance, if the building has N floors, the FSY will have a value of from 0 to N-1.
FIG. 11 is a view showing the correlation among a floor level 11B, a position point 11A corresponding to FLHD and a position point 11C corresponding to FLHU for each floor. In this embodiment, an operation point for output from the second position detecting device (DZU) 22 lies within the range from 150 mm below floor level to 250 mm above floor level, and an operation point for output from the first position detecting device (DZD) 21 lies within the range from 250 mm below floor level to 150 mm above floor level.
FIG. 12 is a flowchart explaining the execution of a program stored in the ROM 94 in FIG. 9. Logical steps in the process of computing the present position of the car are shown. In this FIG. 12, DP indicates the number of pulses to be input to the microcomputer 18. For example, when the microcomputer 18 is computing with a period of 50 ms, the DP indicates the number of pulses, which are input through the route from the pulse generator 16 to the counter circuit 17 and further to the microcomputer 18 within this period of 50 ms.
The logical sequence, needed for the execution of the program stored in the RAM 94, will now be described with reference to FIG. 12. In step S121, the sequence decides whether the car 11 is in motion or not. If the car 11 is in motion, the sequence goes down to step S122, where the sequence decides whether the car 11 is traveling upward or downward. If the car 11 is traveling upward, the sequence goes to step S123, and if the car 11 is traveling downward, the sequence goes to step S126.
In the step S123, the present position SYNC of the car 11 can be computed with the following operation expression: EQU SYNC.rarw.SYNC+DP
In step S124, the sequence decides, with the following operation expression, whether the car 11 has traveled past a position, midway between two floors: EQU SYNC.gtoreq.(1/2)[FLHL(FSY)+FLHL(FSY+1)]
If the car 11 has traveled past that position, the present floor FSY of the car 11 is updated in step S125 as follows: EQU FSY.rarw.FSY+1
But if in step S122, where the sequence decides whether the car 11 is traveling upward or downward, the car 11 is found to be traveling downward, the sequence goes to step S126, and the present position SYNC of the car l1 is updated in the following operation expression: EQU SYNC.rarw.SYNC-DP
In step S127, the sequence decides, with the following operation expression, whether the car 11 has traveled past a position midway between two floors: EQU SYNC&lt;(1/2)[FLHL(FSY-1)+FLHL(FSY)]
If the car 11 has traveled past that position, the present floor FSY of the car 11 is updated in step S128 as follows: transport. EQU FSY.rarw.FSY-1
As shown in FIG. 13, the car 11 starts moving at time T0, then accelerates, and travels at a constant speed at the time T1 onward. At time T2 a power failure for some reason. Owing to this power failure occurs, the car 11 reduces its speed after time T2 and stops at time T3. Whereas, a power feed to the elevator control apparatus is also cut off at time T2. As a result, the operations immediately stop for the pulse generator 16, the counter circuit 17 and the microcomputer 18, all of which are essential to the elevator control apparatus. Therefore, the distance, which the car 11 travels between the two points time T2 and T3, does not affect the computation for the present position of the car 11. That is, more specifically, the distance, corresponding to the shaded portion in FIG. 13, between time T2, when the power failure occurs, and T3, when the car 11 stops, does not affect the computation for the present position of the car 11. For this reason, even if a SYNC value, corresponding to the present position of the car 11 prior to the power failure, is stored in the RAM 95, which is supported with the backup battery power supply 96, the SYNC value has error, by the amount shown in the shaded portion of FIG. 13, at the recovery from the power failure.
Consequently, such a conventional elevator control apparatus is so constructed that the car 11 travels down to the bottom floor for a time. A fixed speed reduction apparatus for the bottom floor controls the speed reduction when the car 11 travels towards the bottom floor. Once the car 11 reaches the bottom floor, the bottom floor detecting device 25 shown in FIG. 8 engages the cam 26 of the car 11. A signal responding to this engagement is transmitted to the microcomputer 18. The followings are performed to correct the present position of the car 11 and the present floor where the car 11 rests. EQU SYNC.rarw.FLHL(0) EQU FSY.rarw.0
As is recognized from the above-described reasons, the conventional elevator control apparatus has the following problems:
(1) Once a power failure occurs, error exists in the information about the present position of the car and the floor where the car rests at the recovery of the power failure.
(2) To compensate for the error, the car should travel down to a standard floor (for example, the bottom floor) for a time. On the standard floor, the computation is performed for the information about the position of the car and the floor where the car was at the time of the power failure in order to correct this information. For this reason, even at the time of recovery from the power failure, the elevator is not put back into normal service, and is forced to travel down to the standard floor.
(3) In case of a power failure during the travel of the car, an expensive backup power supply is required to stop the car completely.